The T-Maxx 2.5 (.15 ) shows about 1 to 1.1 H.P. on the dyno...it's a "small block"

The .28 is a "big block" and substantially larger.

The T-Maxx has a cast alum. "cradle" that holds the engine, and that assy. bolts to the chassis plate.

You'd have to check around, in the car/truck engines forum to ask some of the guys over there if there's an engine mount cradle assembly or adapter that would hold the .28 to allow it to work with the T-Maxx chassis...

I put an SH .28 in a Savage a while back...it's a good running engine, similar to the Dynamite Mach .26 and the XTM 24/7 but it's not a 3.5 H.P engine...I haven't seen that particular engine on the dyno, but the other 2 have checked in at around 2 to 2.2 actual H.P. IIRC